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On Site Guide intelligence

Pirform's intelligence incorporates guidance from the IET's On-Site Guide, specifically Table 7.1(ii). Read more here.

Info

The following applies to flat twin and earth cables. This is wiring type AF in Pirform:

The Pirform wiring type selector showing the flat twin and earth cable type

Ring Final Circuits

The following ring final circuits configurations are recognised as valid by cable-sizing rules.

Rating Standard Live CPC Reference Methods TN-S
30 mA RCD		 TN-S
No RCD		 TN-C-S
30 mA RCD		 TN-C-S
No RCD
30 3036 2.5 1.5 100,102,A,C 106 41zs 106 106
30 3036 4 1.5 100,102,A,101,103,C 171 48 171 138zs
32 CB or RCBO B/C/D 2.5 1.5 100,102,A,C 106 96zs 106 106
32 CB or RCBO B/C/D 2.5 1.5 100,102,A,C 106 NPzs 106 56zs
32 CB or RCBO B/C/D 2.5 1.5 100,102,A,C 106 NPzs 106 NPzs
32 88-2 (60269-2) 2.5 1.5 100,102,A,C 106vd 32zs 106vd 106vd
32 88-2 (60269-2) 4 1.5 100,101,102,103,A,C 171 38zs 106vd 127zs
32 88-3 2.5 1.5 100,102,A,C 106vd 19ad 106 95zs
32 88-3 4 1.5 100,101,102,103,A,C 171 22zs 171 112zs
32 CB or RCBO B/C/D 4 1.5 100,101,102,103,A,C 171vd 114zs 171vd 171vd
32 CB or RCBO B/C/D 4 1.5 100,101,102,103,A,C 171vd NPzs 171vd 66zs
32 CB or RCBO B/C/D 4 1.5 100,101,102,103,A,C 171vd NPzs 171vd NPzs

The following abbreviations are used in the table above:

  • CB: Circuit breaker
  • RCBO: Residual current circuit breaker with overcurrent protection
  • TN-S: Terra neutral - separate
  • TN-C-S: Terra neutral - combined and separate
  • RCD: Residual current device
  • vd: Voltage drop
  • ad: Adiabatic limit
  • zs: Earth fault loop impedance
  • sc: Line to neutral
  • NP: Not permitted
  • NPvd: Not permitted (prohibiting factor: voltage drop)
  • NPad: Not permitted (prohibiting factor: adiabatic limit)
  • NPzs: Not permitted (prohibiting factor: earth fault loop impedance)
  • NPsc: Not permitted (prohibiting factor: line to neutral)